Laser-Induced Ocular Lesions with Thulium Fiber Laser in Endourology: An Ex Vivo Study

The thulium fiber (Tm-F) laser is currently studied as an alternative to the holmium: yttrium-aluminum-garnet (Ho:YAG) laser, the gold standard for endocorporeal laser lithotripsy. We aimed to evaluate the ex vivo effects of an accidental Tm-F laser exposure on bovine eyes and to test the protective action of different eyeglasses in preventing eye lesions in case of an accident. A 50-W TFL generator (IPG Photonics^®, Russia) with a wavelength of 1940 nm and 200-μm core diameter fibers (CDFs) were used. The laser fiber tip was pointed perpendicularly at different distances (0, 1, 3, 5, 8, and 10 cm, respectively) to the pupil center of the bovine eye. The Tm-F laser was activated for 1 or 3 seconds at three different settings (0.5 J-20 Hz, 1 J-10 Hz, and 2 J-10 Hz, respectively). The experiment was repeated using laser safety glasses and eyeglasses. After lasering, eye samples were immersed in a 0.5% fluorescein serum (Faure-Ciba-Geigy^®, Switzerland), then rinsed with saline. White and blue light examination looked for localized epithelial burns (LEBs), extended epithelial burns (EEBs), superficial corneal ulcerations (SCUs), and deep corneal ulcerations (DCUs). A total of 68 bovine eyes were used. Despite the laser settings, both DCU (contact) and SCU (1 cm) developed without eye protection for 1 and 3 seconds of lasering. At the 3-cm fiber-eye distance, only burning lesions were observed. Over 5 cm, no lesion was found. At contact or 1-cm fiber-eye distance, pulse energy did not change the lesion grade, but at 3 cm, high pulse energy led to higher grade corneal lesions (0.5 J-10 Hz:LEB; 1 J-10 Hz:EEB). Despite the fiber-eye distance, no corneal lesions were reported in the laser safety glass or eyeglass group for 1 second of laser exposure. Our study highlights the risk of eye damage caused by Tm-F. Without proper eye protection, the Tm-F laser can cause corneal lesions up to 5 cm in distance with 1 second of exposure despite laser settings. Only dedicated protective eyeglasses are effective for long exposures.